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<br />1789 <br /> <br />drainage before the mine-drainage water is discharged to their receiving stre~ms. The pre-treatment (April 1990- <br /> <br /> <br />~Ch 1992) and post-treatment (AprilI992-March 1993) dissolved and total-recoverable trace-element . <br /> <br />concentration data were compared for statistical differences with the Wilcoxon rank-sum test. Statistical testing on <br /> <br />flow-adjusted concentrations was not performed because of the absence of any statistically significant explanatory <br /> <br />variables for metal concentrations. The instantaneous streamflow associated with the water samples collected <br /> <br />during the pre-treatment and post-treatment periods were also tested for significant differences with the Wilcoxon <br /> <br />rank-sum test. It was assumed that streamflow had no statistically significant effect on the distribution of trace- <br /> <br />element concentrations during the two periods because no significant difference was detected between pre- <br /> <br />treatment and post-treatment instantaneous streamflow (T.A. Cohn, U.S. Geological Survey, oral commun., 1995). <br /> <br />.e' <br />. . <br /> <br />:;Ji~~~~%'I~!Mt!~ Ir!l~~~'~'f'- <br />:. jj;"IIo!IJJ UI';J;Wj! U~~..a U.IiIioIifGf" <br />Subject to Revision' <br />DO NOT QUOTE OR RHEAS;: <br />rending Approval by Director, <br />U.S. Gsc!ogicol Survey <br /> <br />. <br /> <br />19 <br /> <br />-_..,...".,". <br />